As one type of an image forming apparatus, there is known an image forming apparatus equipped with a so-called decoloring apparatus that prints an image on a sheet with the use of a recording material, for example a decolorable toner, and carries out a decoloring processing on the toner for forming the image through heating with a fixing device to erase the image printed on the sheet in order to reuse the sheet on which the image is formed.
Such an image forming apparatus is used for various purposes including an image forming process for forming an image with the decolorable toner, an image forming processing for forming an image with a non-decolorable toner and an erasing process of the image formed on a sheet with the decolorable toner. The foregoing processing is realized by applying heat to the images formed on the sheet. In other words, it is necessary to set a plurality of temperatures such as a temperature necessary for fixing the decolorable toner, a temperature necessary for fixing the non-decolorable toner and a decoloring temperature necessary for erasing the image formed on the sheet with the decolorable toner to enable the image forming apparatus to operate.